In an internal combustion engine, the combustion gas produced in the combustion chamber inevitably leaks to the crank chamber owing to the combustion pressure produced in the combustion chamber. The combustion gas that has leaked to the crank chamber is known as blow-by gas, and is typically recirculated to an intake passage via a breather device by using the negative pressure in the intake passage. The breather device is provided with a breather chamber for removing oil mist from the blow-by gas drawn from the crank chamber via a breather passage. Also, for the purpose of positively displacing the blow-by gas from the crank chamber, fresh air may be introduced into the crank chamber via a fresh air introduction passage. Since the blow-by gas may flow out of the crank chamber via the fresh air introduction passage in the opposite direction to that of the fresh air, the fresh air introduction passage may be provided with a fresh air chamber for separating oil therefrom. See JP2015-094239A, for instance.
FIG. 11 of JP2015-094239A illustrates a breather device provided with a breather chamber separated into a first gas liquid separation chamber located on the upstream side and communicating with the crank chamber, and a second gas liquid separation chamber located on the downstream side and communicating with the intake manifold. A part of the bottom wall of the first gas liquid separation chamber is provided with an oil return hole for returning the separated oil back to the oil reservoir (oil pan) of the engine, and an auxiliary opening is provided adjacent to the oil return hole for communicating the first gas liquid separation chamber with the valve actuation chamber. The oil return hole also serves as a breather passage for communicating the crank chamber with the first gas liquid separation chamber. Thereby, even when the blow-by gas is voluminous, and a relatively large amount of oil is separated in the first gas liquid separation chamber, the breather passage is prevented from being clogged by the separated oil so that the blow-by gas is allowed to be introduced into the breather chamber in a favorable manner without fail.
When a vehicle corners or accelerates/decelerates, the oil contained in the oil reservoir is subjected to an acceleration so that the oil level in the oil reservoir tilts with respect to the engine. As a result, the upstream end (lower end) of the breather passage may be submerged in the oil. In such a case, the oil of the oil reservoir may be drawn upward in the breather passage, and may even reach the breather chamber. If an auxiliary opening is formed in a bottom part of the breather chamber as disclosed in JP2015-094239A, the negative pressure in the breather chamber is weakened by the air drawn from the valve actuation chamber into the breather chamber via the auxiliary opening so that the rise of the oil into the breather chamber can be avoided.
However, since the auxiliary opening is provided in a part of the bottom wall of the breather chamber adjacent to an upstream end part of the breather chamber, the auxiliary opening may be flooded by the oil when a large amount of oil is present in the first oil separation chamber so that the negative pressure may not be weakened so much as desired. This may be avoided by increasing the size of the auxiliary opening, but the oil splashed in the valve actuation chamber may be drawn into the breather chamber along with gas due to the large opening area of the auxiliary opening.